Chicken Or Egg ? Scrambled Or Over Easy?


1999 Dodge Intrepid

2.7L V-6 Auto

200,000 + Miles

Havoline 5w30 consumption slowly increasing over the years and is currently passing through 1 qt / 2,000 miles


Have spent almost nothing on car in over ten years except DIY maintenance. Car owes me nothing.

I did get a MIL and code PO133 two years and tens of thousands of miles ago. Bank 1 Sensor 1 was right in my face so I screwed in a new Bosch oxygen sensor. Case closed.

Fast forward to 2 weeks ago. MIL on and PO133 is back. I Turned it off and waited. After a couple of drive cycles PO133 is back and brought a friend . . . PO420 Catalyst Deficient . . . Makes sense.

I turned off the MIL to see if it would be back right away (I’ve had cases where codes never come back).

A couple drive cycles later . . . Mil on, but NO returned codes, just a NEW one. I now have ONLY PO404 EGR Valve.


What do you suppose is going on here?

Is there a symbiotic relationship . . . or coincidence ?

Is the EGR valve the culprit or the victim ?

Is the O2 sensor or converter a suspect or victim ?

Oil poisoning ?

Recommendations or theories ?

This was my wife’s 100 mile per day daily driver and just got replaced, but I’d like my almost 16 year-old daughter to drive it. Am I dreaming ?


Oops, I Forgot Something.
The Car Is Running Well And Always Has.


Well, the simplest thing to do would be cleaning the EGR valve and resetting the codes and waiting

Thanks, That’s A Plan. The EGR Is Electrically Operated. I’m Going To Get A Price On One In Case It’s Fairly Inexpensive. I’d Just Replace It In Case The Electric Part Is Going South, Otherwise, Clean It.

I do realize the DTCs do not specify part replacements, rather which system has faulted, but on parts that are fairly easy and inexpensive to replace and subject to deteriorate or wear with miles and age, it sometimes makes sense.


Drive it

Thanks, That’s A Plan, Too, But I Don’t Want A Plugged Converter If That’s What The Codes Are Warning Me Will Happen.


CSA - is this a quiz? seems to me you already know the solution and you are wondering if others can figure it out.

Quiz ? Answer ? Absolutely Not. I’m Wondering If There’s A Pattern Here, A Cause And Effect Order Of DTCs Or System Failures. I’m Open To Ideas And Suggestions So I Know How To Proceed.

Is it time to take it in to a “real technician” with a “real scanner” and have some “real time” data translated ?


My theory: the EGR valve is sticking open. The stuck open valve is feeding exhaust gas when it shouldn’t. The exhaust gas is being read by the O2 sensors and that has set off P0133 & P0420. The computer may have picked up on the out of spec O2 sensor readings before the EGR problem just b/c computers are dumb and can really only do what they’re programmed to do. The “rules” for kicking up the P0404 are probably a little more stringent (in terms of drive cycles or time or whatever) that those that relate to O2 sensor readings.

Either way, I’d never deal with a code related to O2 sensor readings with a known exhaust system problem (such as EGR).

That EGR valve is probably not cheap. So I’d check and triple check the wiring harness & connector. Then clean and double clean the mechanical aspects of the valve (without damaging the electronics), and then - to the extent possible - check and double check the valve’s electronic function before replacing it. …Oh - and whatever system of tubes or pipes or whatever that feed it, and any other related sensors or whatnot (I just don’t know the specifics of this system).

Thanks, Cigroller. I Appreciate Your Taking Time To Read Through My Question And Come Up With A Thoughtful Theory That Looks At The Chronology Of Events. I Had Similar Thoughts.

You’ve given good advice about the O2 code and I will triple check the connector and what I can of the wiring.

Since an EGR is about $150 new, (which wouldn’t be bad on a newer, more valuable car), I think I’ll head over to my local Auto salvage/recycling yard and see if they’ve got a “younger” EGR valve for a few bucks. (These cars are pretty easily found there.) I like doing that because I can practice parts R&R on a cadaver Dodge before I tear into an already operable car. If I get one, I’ll get it thoroughly cleaned up the best I can and have it ready for transplant.

Doesn’t look like rocket science, just a tad difficult (top of engine, but behind right head - FWD car, but engine is longitudinal, not transverse). Looks like just four bolts out, 2 more after removal (pipe attachement), 3 new gaskets, and done, if everything unscrews. I’ve got a factory manual and pretty good tool selection.

"Code PO404 - EGR position sensor signal does not correlate to EGR duty cycle."
I can’t find info on the EGR position sensor. Do you think it’s an integral part of the EGR valve ? That’s what I’m thinking.

I’m still open to any other ideas or suggestions.


you have an egr code because your cat is partially plugged.

Pete, Thanks. Will You Elaborate On Your Suggestion, Please. I’m Listening. I’ve Thought About This Possibility. Are You A Professional Tech ?

Would obstructed flow through the cat obstruct inhibit flow through the EGR system ? Am I thinking right ?

If I shoot both cats with my infrared non-contact themometer would the partially plugged converter be hotter after the car is brought to operating temperature ? Both converters (right bank and left bank) are visible and temp gun accessible under the hood.


I’d guess that your converter is not plugged. I’d guess that you have carbon desposition on the EGR valve itself, causing it to stick and tripping the EGR system codes, and the source of that despoition (burning any oil?) has also coated the catalyst in the converter and possibly the oxygen sensor as well. Both need to be clean enough to get good contact with the exhaust gasses. Coating will adversely affect both.

I think your first guesses were the best. I think the EGR system, the oxygen sensor, and perhaps the cat comverter are all victims of carbon deposition.

TSM, Thanks. I’ve Got A New Theory After My Trip To The Local Automotive Bone Yard. It Goes Along With Your Theory.

I wrestled (Arrrgg . . . ) 2 EGR systems (valve and plumbing) from 2 cadaver Dodges (15 bucks for both). I’ve got a little drilling and tapping to do. Those little 6 mm screws that attach one pipe to the valve don’t hold up to years of hot/cold cycling and scaley rust.

What I found in the cadavers was hardening of the arteries (pipes). They both had quite a bit of “cholesterol” (oily, goopy sludge and carbon build-up) on the walls of the two EGR pipes, the one from the exhaust manifold to the valve and the one (it Y’s) that goes from valve to two sides of plastic intake.

I now suspect that the valve itself may not be the problem (although I will clean it up). It might be an arterial “cholesteral” deal.

So, I’m going to take the cadaver systems apart, clean them up thoroughly, tap as necessary, buy a couple gaskets, and get all ready for transplant in my wife’s car.

She’s been driving the thing on her 100 mile daily rides when the roads are crappy so her new Impala is safe at home (she’s not as checked-out in it, yet). I’ve gotten only a new PO401 - EGR flow insufficient and another PO404, mentioned above.

Can you tell I’m thrifty and enjoy a challenge ?


Yours may actually look better than the ones you pulled, but probably you’re on to something.

Obviously you maintain your engine, as you’ve had none of the problems others have had with oil sludging on this engine. Obviously all it takes is oil changes when you’re supposed to.

Oblivion, Thanks. This Baby Does Do A Little Consuming Though, Oil That Is, Texas Tea.